Population genetics of Japanese monkeys: I. Estimation of the effective troop size.

In order to estimate the genetically effective troop size of Japanese monkeys, we have to know the pattern of distribution of the numbers of gametes contributed by the individual members of the parental population to the next generation. The author inspected the observation records of macaque troops made by a number of socio-ecologists and found that the relationship between sexual rank and sexual activity of adult males could be approximately expressed by the law of geometrical series. Assuming that the genetic contribution of male parents to the next generation was proportional to their sexual activity and that the numbers of gametes contributed by the female parents formed thePOISSON distribution, the author derived a formula for estimating effective troop size (N), namely, whereN c was the census number andN m andN f the numbers of male and female parents, respectively, of the troop. Moreover, assumingN m =0.2N c andN f =0.3N c as an average, the effective size could be estimated as 36% or less of the census number.